The present disclosure relates to aspects of head suspension assemblies as are utilized for movably supporting a head within a disk drive, and in particular to head suspension assemblies that include piezoelectric microactuators for fine head movement and control.
Hard-disk drives (HDDs) are examples of data storage devices that include one or more rotatable disks to which data is written and read by way of magnetic read/write transducer heads that are movably supported with respect to surfaces of the disks by a corresponding number of head gimbal assemblies (HGAs) that can together form a head stack assembly of HGAs. One HGA is typically movably supported relative to a respective disk surface so that a magnetic read/write head can be selectively positioned relative to a data track of the disk surface. Such magnetic head is typically provided on an aerodynamically-designed slider so as to fly closely to the disk surface, at a so-called “fly height,” of several nanometers above the disk surface while the disk is spinning. Each HGA is typically connected to a rotatable drive actuator arm for moving a read/write head and slider including a flexure or gimbal over the disk surface for data writing and reading. Each actuator arm is connected to be driven by a voice coil drive actuator servomechanism device. Such an assembly allows each magnetic read/write head to be independently controlled for positioning relative to specific data tracks of a disk surface.
As HDD data storage needs have increased, typical data track density on disk surfaces has also steadily increased in order to obtain greater data storage within a given disk surface area. This disk surface density is commonly referred to as areal density. Specifically, the data tracks themselves have become narrower and the radial spacing between tracks has decreased in order to increase disk areal density.
In order to improve fine movements of a magnetic read/write head as provided to a slider of a HGA, and to obtain greater data resolution, various servo actuators have been developed and employed in HDD applications. In general, a voice coil drive actuator provides a coarse movement for positioning of the magnetic read/write head to the data tracks. If a finer movement is also desired, a microactuator can then provide a second, finer movement for resolution of data tracks within high density HDDs. Such systems are referred to as dual-stage servo-actuated suspension systems.
Presently, drives that use a dual-stage actuation may utilize head-level microactuation during conditions like servo-fault, “buzz” conditions, factory bode sweeps, etc. Head-level microactuation may also be referred to as co-located microactuation. The placement of a microactuator within the HGA often leads to challenges in terms of design, performance and manufacturability. Head-level co-located microactuation may also include independent actuation of a slider and/or surrounding structures, which may be flexibly connected to an articulated microactuator arm through a rigid load beam.
A microactuator typically includes and makes use of one or more elements composed of piezoelectric crystal material, such as lead zirconate titanate (PZT). Other such elements can be strategically provided at one or more locations along an HGA, and may be provided in symmetric pairs for use in deflecting and deforming the HGA or parts thereof. An HGA typically includes a baseplate for connection with an actuator arm, a load beam including a baseplate portion, a spring portion and a rigid region, and a flexure (or alternatively, a gimbal) that supports a slider with a magnetic read/write head and that allows the head to pitch and roll about a dimple on the load beam. The interconnection of the flexure and load beam allow for pitch and roll movement of the aerodynamically-designed slider relative to a spinning disk surface as the slider flies on an air bearing created by the spinning disk.
Microactuators have been developed to work in conjunction with and be structurally connected to various HGA components, such as baseplates, load beams, and flexures. Microactuators are generally configured to cause a distortion of material, typically stainless steel, by providing an electric field across one or more fixed elements of piezoelectric material. A controlled application of a voltage difference across a piezoelectric microactuator, such as PZT, causes the piezoelectric microactuator to expand or contract, in order to distort the baseplate, load beam, or flexure, and thus controllably provide a fine movement of the slider and head with respect to a specific data track on the disk. An application of electric signals to PZT produces a deformation, and conversely, a deformation in the PZT produces an electric signal.
Microactuators can be structurally provided in symmetric, lateral pairs for controlled deflections. A microactuator pair can act together by applying similar magnitude but opposite polarity electric fields to the associated piezoelectric element pair depending upon the location and arrangement of the piezoelectric element pair. Typically, a microactuator pair includes a pair of PZT elements. The two paired PZT elements are identical to each other, with the exception of poling direction. So, when a positive voltage is applied to both the PZTs, one element expands or lengthens, while the other element contracts or shortens, transmitting a lateral motion to the head.
In order to controllably actuate such piezoelectric microactuators, positive and negative electrical connections are generally provided to each of the pair of piezoelectric microactuators. Conductors are typically provided along HGAs, extending to the head for read/write functionality, and for providing voltage across the piezoelectric microactuators of a dual-stage actuated head suspension.
Depending on the location and positioning of the microactuators, the suspensions (e.g., HGAs) are generally classified as “load beam bias” microactuator-based suspensions or “co-located” microactuator suspensions. In a load beam bias type microactuator HGA, the microactuators are located on the load beam, near the baseplate. In a co-located type microactuator HGA, the microactuators are located in an area at slider end of the HGA. The moment caused by forces from the microactuators are transmitted to the slider through the load beam.
In a co-located microactuator-based HGA layout, a pair of microactuators are typically located near the slider and are connected to the flexure (e.g., a gimbal). The moment forces from microactuation are transmitted to the slider through the flexure. An electrical input to each of the microactuators of the pair may create an equal and opposite movement between them, leading to a lateral movement at the slider, transmitting through the flexure.
Each of the discussed mentioned microactuation configurations has respective advantages and challenges, and the choice of microactuation configuration may significantly influence the driving and control schemes used by a servo actuation system. The load beam bias microactuator-based suspension generally provides the advantage of larger displacement per unit input. However, greater reaction forces transmitted back to the actuator arm may excite or cause undesirable resonances and a degradation of tracking performance. The co-located microactuator-based suspension generally provides the advantage of minimizing the reaction forces on the actuator arm (at typical tracking frequencies) by providing a pivot about the dimple on the load beam, however, has the challenge of lower displacement per unit input voltage. As a result, it is challenging to implement in a design that requires a relatively large range of head motion while maintaining a desirable degree of reaction force feedback through the actuator arm.
Resonance can include a vibration of large amplitude in a mechanical or electrical system caused or contributed to by a relatively small periodic stimulus of the same or nearly the same period as the natural vibration period of the system, and the adjustment thereof. Vibration and resonance at various frequencies can be measured in displacement, which can produce a corresponding and resultant voltage. As a shortcoming of existing configurations, undesirable resonance or other vibration at a head may cause various inefficiencies related to writing or reading magnetic media. For example, undesirable resonance may cause offtrack errors or interfere with servo performance. In some cases, undesirable resonance can cause slider-disk contact which may lead to catastrophic failure of the disk and/or drive. Existing microactuation structures choose between sensing and actuation using the microactuator set associated with an HGA. Therefore, there is a desire to control for undesirable resonance within HGAs of HDDs.